Multi-well microfiltration apparatus and method for avoiding cross-contamination

Abstract

The present invention provides multi-well plates and column arrays in which samples (e.g., cell lysates containing nucleic acids of interest, such as RNA) can be analyzed and/or processed. In one embodiment, the microfiltration arrangement is a multilayer structure, including (i) a column plate having an array of minicolumns into which samples can be placed, (ii) a discrete filter element disposed in each minicolumn, (iii) a drip-director plate having a corresponding array of drip directors through which filtrate may egress, and (iv) a receiving-well plate having a corresponding array of receiving wells into which filtrate can flow. The invention provides multi-well microfiltration arrangements that are relatively simple to manufacture and that overcome many of the problems associated with the prior arrangements relating to (i) cross-contamination due to wicking across a common filter sheet or (ii) individual filter elements entrapping sample constituents within substantial dead volumes. Further, the invention provides multi-well microfiltration arrangements that adequately support discrete filter elements disposed in the wells without creating substantial preferential flow. Additionally, the invention provides multi-well microfiltration arrangements that avoid cross-contamination due to aerosol formation, pendent drops and/or splattering. Other disclosed features of the invention provide for the automated covering or heat-sealing of filtrate samples separately collected in an array of wells.

It is claimed:  
     
       1. An apparatus for avoiding cross-contamination due to pendent drops of fluid hanging from a plurality of discharge conduits disposed in an array above a corresponding array of receiving wells, comprising: 
       (i) a carriage configured to carry one of said arrays and adapted for linear reciprocal motion in either of two directions along a first, generally horizontal, axis from a neutral position whereat said arrays are substantially axially aligned;  
       (ii) a stepper motor;  
       (iii) a linkage assembly mechanically communicating said stepper motor with said carriage such that each rotational step of said stepper motor induces movement of said carriage a given distance from said neutral position in one of said two directions depending upon the direction of angular rotation of said motor, thereby effecting relative motion between said discharge-conduit array and said receiving-well array such that pendent drops of fluid hanging from said discharge conduits are simultaneously touched-off to inner sidewalls of corresponding receiving wells; and  
       (iv) a compression spring mounted within said linkage assembly in a manner permitting said spring (a) to provide a predetermined amount of resistance to movement of the carriage from said neutral position, and (b) to compensate or absorb linear overshoot due to excess angular rotation of the motor beyond the amount required to move the discharge conduits into firm abutment with the inner sidewalls of the receiving wells.  
     
     
       2. An apparatus for avoiding cross-contamination as recited in  claim 1  further comprising: 
       a vacuum chamber communicating with said discharge-conduit array from a side thereof opposite said receiving-well array, whereby evacuation of said vacuum chamber is effective to urge pendent drops of fluid hanging from said discharge conduits in a direction away from said receiving wells and into said discharge conduits.  
     
     
       3. An apparatus for avoiding cross-contamination as recited in  claim 1 , wherein said carriage is configured to carry said discharge-conduit array. 
     
     
       4. An apparatus for avoiding cross-contamination as recited in  claim 3 , further comprising: 
       a vertical positioning assembly disposed on said carriage and supporting said discharge-conduit array for linear movement along a second, generally vertical, axis between a lowered position whereat said discharge conduits extend down into respective receiving wells and an elevated position whereat said discharge conduits clear said receiving wells.  
     
     
       5. A method for avoiding cross-contamination due to pendent drops of fluid hanging from a plurality of discharge conduits disposed in an array above a corresponding array of receiving wells, comprising: 
       (i) touching-off, in a substantially simultaneous fashion, said pendent drops of fluid hanging from said discharge conduits to inner sidewalls of respective receiving wells; and  
       (ii) drawing said pendent drops of fluid hanging from said discharge conduits in a direction away from said corresponding receiving-well array and into said discharge conduits.  
     
     
       6. The method of  claim 5 , wherein said step of touching-off is effected by shifting the discharge-conduit array along a plane substantially orthogonal to the longitudinal axes of the receiving wells, while the receiving wells are maintained in a substantially fixed position. 
     
     
       7. The method of  claim 6 , wherein each of said discharge conduits is shifted into contact with one sidewall portion of a respective receiving well, and then is shifted into contact with another, laterally opposing sidewall portion of the same receiving well. 
     
     
       8. The method of  claim 7 , wherein a stepper motor is stepped in order to shift said discharge-conduit array, said stepper motor disposed in mechanical communication with said discharge-conduit array such that angular rotation of said stepper motor induces linear motion of said discharge conduits. 
     
     
       9. The method of  claim 5 , wherein said step of drawing pendent drops of fluid is effected by establishing a reduced pressure above said discharge conduits. 
     
     
       10. The method of  claim 5 , wherein an upstanding upper end region of each of said discharge conduits is received within a respective column, thereby forming an array of microfiltration wells; and wherein each column has (i) a first inner bore defining a lumen within the column, and (ii) an end region defining (a) a second inner bore having a diameter greater than that of the first inner bore and (b) a transition region that joins the second inner bore to the first inner bore; and wherein a filter element is disposed in each column, said filter element held in compression between the transition region of the column and the upper end region of a respective discharge conduit.